The present invention is concerned with ceramics, and more particularly with a nepheline syenite and leucite-containing ceramic raw material and ceramic bodies made therefrom. Although not limited thereto, the invention has particular application to a ceramic raw material comprising a dental porcelain powder and to dental porcelain made therefrom, which porcelain has a nepheline syenite glassy phase matrix in which is dispersed a crystalline leucite.
The use of nepheline syenite in dental porcelains as a replacement for feldspar is known, as shown in The Ohio State University Eng. Exp. Sta. Bulletin 118, Mar. 19, 1944 and U.S. Pat. No. 2,334,319. The use of nepheline syenite in glass or for other ceramic purposes has also been suggested. Am. Mineralogist 31, 284-87 (1946).
Leucite is a naturally occurring mineral which heretofore has not been considered to be commercially important (see Ceramic Industry Magazine, page 76, January, 1974) and is not believed to be available in commercial quantities. Insofar as is known, leucite has not been included in ceramic compositions although it is conceivable that isolated colonies of leucite may be formed in some ceramics during fusing thereof. Laboratory preparation of leucite has been reported in the literature, American Journal of Science, Vol. 253, December 1955. pp. 681-746. Also see, J. Chem Soc. 1955, 2480-1, abstracted in Chemical Abstracts, Volume 49, columms 13727-13728.
In providing ceramic raw materials and the ceramic bodies made therefrom, it is generally desirable that the body have characteristics of good strength, thermal expansion and appearance. (As used herein and in the appended claims, the term "ceramic raw material" means the ingredients which are fired to form ceramic bodies, and the term "porcelain" has its usual meaning of a white, fine grade of ceramic.) Strength and thermal expansion characteristics are particularly important in ceramics used in applications such as dental porcelain. In dental porcelains, thermal expansion and other characteristics of the porcelain must be rigidly controlled to insure good bonding of the porcelain to the metal components of the dental prosthesis and control of the exacting dimension and configuration requirements. Obviously, high strength and controllable thermal expansion characteristics are generally desirable characteristics in any use to which the ceramic is put.
It is accordingly an object of the present invention to provide a novel ceramic raw material composition which, when fused, provides a ceramic body of high strength and rigidly controllable thermal expansion characteristics.
It is another object of the present invention to provide a novel ceramic raw material composition essentially containing leucite and nepheline syenite and a novel method of making ceramic bodies using the composition.
It is yet another object of the present invention to provide a novel ceramic body which includes a leucite crystalline phase dispersed in a matrix of a glassy nepheline syenite phase and possibly other ingredients, which provides the ceramic body with high strength and controllable thermal expansion characteristics.
It is yet another object of the present invention to provide a ceramic raw material containing a pre-formed synthetic, i.e., manufactured, leucite and ceramic bodies made therefrom in which the leucite in combination with the other ingredients provides the ceramic bodies with high strength, good appearance, and good controllable thermal expansion characteristics which are well suited for use as dental porcelains.
Another object of the invention is to provide a novel method for making ceramic bodies which are suited for use as the porcelain component of dental prostheses.
Other objects and advantages of the present invention will become apparent from the following description.